Heat Acclimatization and the Encyclopedia of Sports Medicine and Science

The online Sports Science Journal is a growing resource for all athletes and coaches. As part of this site they are building an on-line encycolpedia of sports medicine and science. There are a few posts that are useful at this time of year for many of us. Heat Acclimatization and Jet Lag are two that come to mind in the competitive summer season - for those of us in the Northern Hemisphere at any rate!

One wonders if they are considering moving to a wiki-format to allow more people to edit the articles on the site and allow it to grow a bit faster - but I expect the desire to kep the site on par with peer-reviewed journals in print will prevent a shift to wiki.

Heat Acclimatization

The Heat Acclimatization article notes that the body does indeed adapt to exercise in the heat. It takes 14 days for complete adjustment - but that different body systems change at different rates. The adaptaions in days 1-5 improve cardiovascular control, such as an increase in plasma volue, while in later days 5-8 thermoregulatory adaptations are maximized - combining the cardiovascular control with increased sweat rates and earlier onset of sweating. Sodium Chloride (salt) losses in sweat decrease in days 3-9. It is interesting to note that several of the adaptations appear to be to maintain short-term stability as after complete adaptation occurs things like salt losses in sweat and plasma volume return to pre-acclimatization levels. One wonders if, like altitude training, a period in a hot humid environment could provide some temporary improvements useful after return to a normal environment. Indeed, after acclimatization there is a reduction in muscle glycogen utilization and a decrease in lactate production.

The article also describes the effects of various forms of heat illness. Interestingly, het cramps are mentioned - likely due to a loss of salt. They mention that cramps may be partially a result of drinking "lrage volumes of hypotonic water" - in other words, large volumes of plain water with no electrolytes - as in a spot drink. This is a mild effect, the more serious effect known as hyponatremia and described in a previous post. All forms of heat illness are reduced by acclimatization.

On a related note - while an increase intake of fluids is required in hot enviroments, it does not assist the acclimatization per se - it only mitigates the effects of the heat.

It is noted that the key factor in acclimatization is increased core body temperature - and can be achieved even exercising in cool environments f the intensity of exercise is enough to elevate core temperature. Although I cannot refer to a scientific study, I have read before of Ironman triathletes going to Hawaii training in realitively warm environments wearing excess clothing to simulate the hot humid conditions of Hawaii.

What does this mean for me?

1. If you are going to a hot enviroment to race, you will need to acclimatize for as many as 14 days.
2. Some of this can be done before travelling to the hotter environment by adjusting training intensity, and possibly by ensuring enough clothign is worn to maintain a higher core temperature.
3. If training for long periods of time in a hot environment use a sports drink, not just plain water.

Related posts:

Fluid replacement - when and what should I drink?

Hydration in Rowing

Too Much Water - Hyponatremia

Hydration and Coxies

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